I wish you all a very happy year 2011, may it be rich in halos and celestial wonders!
I ran some simulation of halos created by hollow columns. Usually, hollow columns are considered to be poor halo makers, reducing the probability of getting rare arcs. I have simulated hollow columns display using Zemax.
Zemax is commercial software used for optical design. Its primary purpose is design and optimization of optical systems. It allows only static simulation, but I wrote a few macros to simulate halos. The main advantages are that you don’t need to compute yourself all the optics laws, just to concentrate on the halos, and it is very flexible software. I have been able to simulate displays from twinned and complex crystals. Its main disadvantage is that it is very slow compared to dedicated software like Halopoint. I have compared the two software and they give the same halos, so the optics inside is really the same. Crystals used to simulate hollow columns keep their crystalline faces for the hollow parts. In real crystals, the holes appear to be more rounded and smooth. The halos simulated are so from ideal hollow columns. Simulation shows that, quite unexpectedly, hollow columns strongly enhance complex arcs in the anthelic direction. For instance, Tricker and subhelic arcs are much more prominent than with regular columns. Marko Riikonen pointed out a display with samples showing lots of hollow columns that had strong Tricker and subhelic arc. Simulations with hollow columns are quite consistent with the display.
I still don’t really figure how these complex raypaths can have increased probability with hollow columns, but simulations definitely show it.